I add 2 teaspoons of instant espresso powder to boxed chocolate cake mix and prepare as usual.
1 cup butter
2 1/2 cups powdered sugar
3/4 cup cocoa powder
1 teaspoon vanilla
3 tablespoons cream
In mixer: cream butter, sugar and cocoa until blended. Add cream and vanilla and whip until smooth.
Piped with an 823 star pastry tip